Downhole wireline machining tool string

ABSTRACT

The present invention relates to a downhole wireline machining tool string for increasing an inner diameter of a well tubular metal structure in a well. The downhole wireline machining tool string has a longitudinal axis and comprises a rotatable tool part comprising a machining tool having a first end part, a second end part, a diameter and a circumference, and a stationary tool part comprising a driving unit configured to rotate the rotatable tool part and powered through the wireline. The machining tool comprises a body having an outer face, and the machining tool further comprising a plurality of inserts, each insert having a length along the longitudinal axis, and the inserts projecting from the outer face of the body and being distributed around the circumference. Furthermore, the present invention relates to a machining tool for increasing an inner diameter of a well tubular metal structure in a well or cutting out a piece, e.g. in a downhole valve.

FIELD OF THE INVENTION

The present invention relates to a downhole wireline machining toolstring for increasing an inner diameter of a well tubular metalstructure in a well, the downhole wireline machining tool string havinga longitudinal axis and comprising a rotatable tool part comprising amachining tool having a first end part, a second end part, a diameterand a circumference, and a stationary tool part.

BACKGROUND ART

A casing or a liner in a well often has restrictions such as nipples,no-goes or patches, or restrictions caused by scale or cement on theinner surface, and in order to optimise production e.g. by interveningthe well by a tool, this restriction needs to be removed or at leastdecreased in order to increase the inner diameter of the casing. Anotherpossible restriction may be a stuck valve, such as a ball valve or aflapper valve, at least partly closing the well.

Such restrictions may be removed by means of a wireline tool which isquickly run into the well, but the power available downhole to performthe operation is very limited, which reduces the operation methodsavailable for removing or at least reducing the restriction.

SUMMARY OF THE INVENTION

It is an object of the present invention to wholly or partly overcomethe above disadvantages and drawbacks of the prior art. Morespecifically, it is an object to provide an improved downhole wirelinetool string which is able to remove a metal nipple in a well receivingless power than 8,000 watt.

The above objects, together with numerous other objects, advantages andfeatures, which will become evident from the below description, areaccomplished by a solution in accordance with the present invention by adownhole wireline machining tool string for increasing an inner diameterof a well tubular metal structure in a well, the downhole wirelinemachining tool string having a longitudinal axis and comprising:

-   -   a rotatable tool part comprising a machining tool having a first        end part, a second end part, a diameter and a circumference, and    -   a stationary tool part comprising:        -   a driving unit configured to rotate the rotatable tool part            and powered through the wireline,            wherein the machining tool comprises a body having an outer            face, and the machining tool further comprising a plurality            of inserts, each insert having a length along the            longitudinal axis, and the inserts projecting from the outer            face of the body and being distributed around the            circumference.

The well tubular metal structure to be machined may be partly or fullyrestricted, meaning that the inner diameter of the well tubular metalstructure may be zero at the restriction. By increasing the innerdiameter of the well tubular metal structure, at least part of therestriction is removed.

The restriction may be made of metal, ceramics, rubber, scale, cement orother materials in a well.

The inserts may be fastened directly to the outer face.

Also, the machining tool may be an abrasive machining tool.

Further, the inserts may be abrasive inserts.

Moreover, the inserts may be fastened directly to the outer face withoutany support/backing, such as a steel support.

The inserts may be embedded particles of tungsten carbide, cubic boronnitride (CBN) and/or diamonds, which particles are embedded in a bindermaterial. In this manner, the inserts may be worn while still being ableto machine as new particles will appear, which particles are configuredto proceed with the machining.

Furthermore, the particles may have a grain size of 0.1-1.0 mm.

Additionally, the particles may be distributed in the binder materialthroughout the length, the width and the height of the inserts.

Also, the machining tool may have a bore arranged coincident with acentre axis of the machining tool around which the rotatable tool partrotates.

Further, the bore may be arranged in the body.

Moreover, the inserts may be plate-shaped and project radially from thebody.

Furthermore, the body may have longitudinal grooves in which parts ofthe inserts extend.

In addition, the inserts may be made of tungsten carbide, cubic boronnitride (CBN) or diamonds embedded in a binder material.

Further, the tungsten carbide, cubic boron nitride (CBN) or diamonds maybe in the form of particles having a particle size of 0.01-4.00 mm.

Also, the inserts may extend along the longitudinal axis.

Moreover, the inserts may be soldered, glued or welded to the outer faceof the body.

In addition, each insert may have a width smaller than a length of theinsert.

Additionally, each insert may have a width which is less than 40% of thelength.

Further, the inserts may be distributed along the circumference with amutual distance being at least the width of one insert.

By having a distance between the inserts, the shavings or cuttings fromthe machining process of increasing the inner diameter are able to passthe outer face of the insert abutting the restriction and leave themachining area. When the inserts comprise embedded particles which aremade of tungsten carbide, cubic boron nitride (CBN) or diamonds, theparticles released during the machining process are also able to leavethe machining area. By machining area is meant the area of the inserthaving contact with the restriction.

Moreover, magnets may be arranged on the outer face of the body, closerto the first end part than to the second end part.

Also, the inserts may incline towards at least one of the first andsecond end parts.

Furthermore, the second end part may have a decreasing outer diameter,and at least part of the inserts may extend at least partly along partof the second end part having the decreasing outer diameter.

Moreover, the second end part having a decreasing diameter causes thesecond end part to be round, inclining or tapering.

The inserts may be arranged in succession along the longitudinal axis.

Also, the machining tool may have a bore extending into the second endpart.

Moreover, the bore may be arranged coincident with a centre axis of themachining tool.

The downhole wireline machining tool string may further comprise ananchor section for anchoring the string in the well, or aself-propelling section, such as a downhole tractor, for propelling thestring forward in the well.

Furthermore, the inserts may be arranged in at least a first row and asecond row extending along the circumference, and the first row and thesecond row of inserts may be arranged in succession along thelongitudinal axis.

The first row of inserts arranged closest to the second end part mayhave a smaller outer diameter than the second row of inserts arrangedcloser to the first end part.

Hereby, the inner diameter of the well tubular metal structure can beincreased from a first inner diameter to a second inner diameter by thefirst row of inserts and from the second inner diameter to a third innerdiameter by the second row of inserts. By increasing the inner diameterby means of at least two rows of inserts, the resulting torque issubstantially reduced, as the removal of the material is performed in atleast two steps instead of one.

Furthermore, an outer diameter of the body may be larger opposite theinserts than closer to the first end part.

In addition, the rotatable tool part may rotate less than 300revolutions per minute (RPM).

Also, the rotatable tool part may rotate less than 200 revolutions perminute (RPM).

Also, the driving unit may be powered by less than 7,000 watt.

Moreover, the rotatable tool part may rotate at a low torque.

Finally, the machining tool may increase the inner diameter by millingaway part of a nipple, scale, a sliding sleeve, a whip stock or a valve.

The machining tool may further comprise a fastening element forfastening a machined piece.

Moreover, the body with inserts may be rotatable in relation to thefastening element.

Furthermore, the fastening element may be circumferenting part of thebody, the body being rotatable within the fastening element.

Also, the fastening element may comprise a base part and a projectingpart, the projecting part being more flexible than the base part.

In addition, the machining tool may further comprise a core drill havinga circumferential wall having inserts, said circumferential wallcircumferenting the body and being part of the rotatable tool part.

The present invention also relates to a downhole wireline machining toolstring for increasing an inner diameter of a well tubular metalstructure in a well or cutting out a piece, e.g. in a downhole valve,the downhole wireline machining tool string having a longitudinal axisand comprising:

-   -   a rotatable tool part comprising a machining tool having a first        end part, a second end part, a diameter and a circumference, and    -   a stationary tool part comprising:        -   a driving unit configured to rotate the rotatable tool part            and powered through the wireline,            wherein the machining tool comprises a body having an outer            face and a fastening element for fastening a machined piece.

Moreover, the body may be rotatable within or around the fasteningelement.

Additionally, the fastening element may be arranged in a recess withinthe body.

In this way, the fastening element projects from the inner face of thebody into the bore.

Further, the fastening element may comprise a base part and a projectingpart, the projecting part being more flexible than the base part.

Also, the machining tool may further comprise a core drill having acircumferential wall with inserts, said circumferential wallcircumferenting the body and being part of the rotatable tool part.

The present invention also relates to a machining tool for increasing aninner diameter of a well tubular metal structure in a well or cuttingout a piece, e.g. in a downhole valve, comprising:

-   -   a body,    -   an insert forming a drill bit,    -   a fastening element circumferenting the body, and    -   a core drill having a circumferential wall with inserts, said        circumferential wall circumferenting the body.

Moreover, the fastening element may be arranged within an internalrecess in the circumferential wall.

Furthermore, the body may be rotatable within the fastening element.

Additionally, the fastening element may comprise a base part and aprojecting part, the projecting part being more flexible than the basepart.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its many advantages will be described in more detailbelow with reference to the accompanying schematic drawings, which forthe purpose of illustration show some non-limiting embodiments and inwhich

FIG. 1 shows a downhole wireline machining tool string in a well,

FIG. 2 shows part of a downhole wireline machining tool string inperspective,

FIG. 3 shows a side view of the downhole wireline machining tool stringof FIG. 2,

FIG. 4 shows a perspective view of part of another downhole wirelinemachining tool string having inserts at an end of the machining tool,

FIG. 5 shows a side view of another downhole wireline machining toolstring of FIG. 4,

FIG. 6 shows a perspective view of part of yet another downhole wirelinemachining tool string having inserts at an end of the machining tool anda bore,

FIG. 7 shows a side view of yet another downhole wireline machining toolstring having rows of inserts and thus machining in two steps in onerun,

FIG. 8 shows a perspective view of part of yet another downhole wirelinemachining tool string,

FIG. 9 shows a partly cross-sectional view of part of another downholewireline machining tool string having a fastening element,

FIG. 10 shows a partly cross-sectional view of another machining toolhaving a fastening element,

FIG. 11 shows a partly cross-sectional view of yet another machiningtool having a fastening element, and

FIG. 12 shows a cross-sectional view of yet another machining toolhaving a fastening element internally of the machining tool forfastening of a machined piece.

All the figures are highly schematic and not necessarily to scale, andthey show only those parts which are necessary in order to elucidate theinvention, other parts being omitted or merely suggested.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a downhole wireline machining tool string 1 for increasingan inner diameter ID_(s) of a casing or a well tubular metal structure 2in a well 3. The downhole wireline machining tool string 1 has alongitudinal axis 4 along the extension of the well 3 and comprises arotatable tool part 5 and a stationary tool part 6. The stationary toolpart 6 is arranged closest to a top of the well 3. The rotatable toolpart 5 comprises a machining tool 7 having a first end part 8 arrangedclosest to stationary tool part 6, and a second end part 9 which isarranged by the restriction to be at least partly removed. As shown inFIG. 2, the machining tool 7 has a diameter DT and a circumference CT.The machining tool 7 increases the inner diameter ID_(s) of the welltubular metal structure by machining, such as by milling away part of anipple, scale, a sliding sleeve, a whip stock or a valve in order to atleast partly remove the restriction.

The stationary tool part 6 of FIG. 1 comprises a driving unit 10, suchas an electrical motor, which is configured to rotate the rotatable toolpart 5 and is powered through a wireline 11. The machining tool 7comprises a body 12 having an outer face 14 and a plurality of inserts15. Each insert 15 has a length L (shown in FIG. 3) along thelongitudinal axis 4, and the inserts 15 project from the outer face 14of the body 12.

The inserts 15 are distributed around the circumference CT with a mutualdistance 16 between them, as shown in FIGS. 2 and 3. By having a mutualdistance between the inserts, fluid is allowed to flow past and alongthe inserts and thus flush and cool the inserts, thereby increasing theservice life of the inserts. Furthermore, the shavings or cuttingsreleased during the machining process are able to pass the outer face ofthe insert abutting the restriction and leave the machining area. Whenthe inserts comprise embedded particles made of tungsten carbide, cubicboron nitride (CBN) or diamonds, the particles released during themachining process are also able to leave the machining area.

By machining area is meant the area of the insert having contact withthe restriction, and along the longitudinal axis 4. The machining areaor contact area is less than 60% of the total area of the restrictionand preferably less than 50% of the total area of the restriction. Inother words, if the tool had contact with the restriction along thewhole circumference of the restriction when seen in a cross-sectionalview perpendicular to the longitudinal axis, contact with the wholecircumference is 100%.

As shown in FIGS. 2 and 3, the inserts 15 are plate-shaped and projectradially from the outer face of the body. Each insert 15 is arranged ina groove 18 in the outer face of the body 12 and is fastened to thebody, e.g. by means of soldering. The heat may be applied from withinthe bore of the machining tool. The inserts 15 thus extend from thegrooves 18 and project radially outwards away from the outer face 14 ofthe body 12. The inserts 15 extend along the longitudinal axis so thatthe length L of the inserts extends along the longitudinal axis 4. Eachinsert 15 has a width W_(i) which is less than 40% of the length L ofthe insert, preferably less than 30% of the length L of the insert, morepreferably less than 20% of the length L of the insert, and even morepreferably less than 15% of the length L of the insert. The inserts 15are distributed along the circumference CT, arranged with a mutualdistance of at least the width W_(i) of one insert.

In FIG. 3, the inserts have a curvature and an even thickness alongtheir length. When having a curvature, the inserts function as blades ofa turbine and thus lead or shovel the shadings or cuttings away from themachining area.

In FIG. 2, the machining tool 7 has a bore 17 extending into the secondend part 9. By having the bore 17, the area of the machining tool 7engaging the restriction in order to perform the machining operation,such as by milling or grinding, is substantially reduced, which requiressubstantially less power than a machining tool 7 having inserts 15 allthe way around the front of the tool, as shown in FIG. 4. The bore 17has a centre axis arranged coincidentally with the centre axis and thusthe longitudinal axis 4 of the machining tool 7.

As shown in FIG. 3, the machining tool 7 has a first tool end 19 closestto the stationary tool part 6 and a second tool end 20 closest to thesecond end part 9, and the inserts 15 incline towards the second toolend 20, thereby enabling the inserts to engage the restriction andcentralise the machining tool 7. As can be seen, the inserts 15 alsoincline towards the first tool end 19, which ensures that the inserts donot have any sharp edges which may easily be broken off. The body 12 ofthe machining tool 7 has magnets 33 arranged on the outer face 14 of thebody 12 so that shavings from the machining process adhere to themagnets 33 and are in this way collected and brought up to surfacetogether with the tool string when the tool string is retracted from thewell. The outer diameter ODs of the body is larger opposite the inserts15 than closer to the first end part 8, and the magnets 33 are arrangedin the part of the body having the smaller outer diameter.

In FIG. 4, the second end part 9 of the machining tool 7 has adecreasing outer diameter due to the body tapering, and at least part ofthe inserts 15 extends partly along part of the second end part 9 havingthe decreasing outer diameter. By the second end part 9 having adecreasing diameter is meant that the second end part is round,inclining or tapering and some of the inserts 15 cover part of theround, tapering or inclining end part. The rotatable tool part 5 hasinserts 15 arranged in succession along the longitudinal axis so thatthe second end part 9 is partly covered with inserts in prolongation ofeach other along the longitudinal extension. Inserts 15 are arranged atthe centre of the second tool end 20 of the second end part 9, extendingfrom an end face 21 of the second tool end 20, and further inserts arearranged abutting these centre inserts 15, 15 a and as a prolongation ofthe centre inserts at the inclining face of the second end part 9. Otherinserts 15, 15 c are arranged in prolongation of the inclining inserts15, 15 b, projecting radially from the outer face 14 of the body 12.

In FIG. 6, the machining tool 7 has a bore 17 and first inserts 15, 15′projecting radially from the body 12, and also extending along theinclining surface of the second end part 9. The bore is a centre bore.Thus, when the machining tool 7 machines around a machined piece whichthen enters the bore, no force is spent on grinding the machined piece,only on grinding a circular groove into the restriction to separate themachined piece. In this way, the restriction can be removed by usingonly a small amount of force and with a low RPM. The force is verylimited when operating on wireline several kilometres down the well andthus, by making such a bore, the restriction, so that flow isre-established, can be performed.

The inserts 15 of FIG. 4 are arranged in a first row 22 and a second row23, each row extending along the circumference CT (shown in FIG. 8), andthe first row 22 and the second row 23 of inserts are arranged insuccession along the longitudinal axis 4. The second row 23 of inserts15 acts as a back-up for the first row 22 of inserts, and the inserts ofthe first row 22 are arranged in recesses 24.

When seen from the side of the machining tool as shown in FIG. 5, theinserts may be arranged with different lengths and in an overlappingmanner, and the inserts 15 b arranged closest to the second end part 9have a smaller radial extension than the inserts 15 c arranged closestto the first part 8. The inserts 15 c are L-shaped so as to overlap theinserts 15 b also in the radial direction so that when the inserts 15 bhave machined the restriction from its initial and first inner diameterto a second inner diameter, the inserts 15 c can take over the machiningprocess to machine and increase the inner diameter of the restrictioneven further.

The inserts 15 may be made of tungsten carbide, cubic boron nitride(CBN) or diamonds embedded in a binder material, and the tungstencarbide, cubic boron nitride (CBN) or diamonds may be in the form ofparticles having a particle size of 0.01-2.00 mm. The particles are thusembedded in the binder material. By having smaller bits or particles oftungsten carbide, cubic boron nitride (CBN) or diamonds embedded in abinder material, new bits or particles of tungsten carbide, cubic boronnitride (CBN) or diamonds are always ready to take over when the firstpart of the insert is worn down, and then, new bits of tungsten carbide,cubic boron nitride (CBN) or diamonds will appear to continue themachining process. Thus, the inserts can be used over a longer period oftime, as the inserts function over their entire extension, and machiningtools having these inserts are therefore better able to decrease thethickness of the casing from one inner diameter to a second larger innerdiameter than known tools. Each insert may thus have particles which aredistributed in the binder material throughout the length, the width andthe height of the insert. The inserts are abrasive meaning they are ableto abrade material off a restriction and thus grind part of therestriction.

As can be seen in FIGS. 6 and 12, the inserts 15, 15′ are fasteneddirectly to the outer face 14 of the body 12 of the rotating part andthe inserts are thus fastened directly to the outer face without anysupport/backing, such as a steel support. This enables that the insertsmay be worn down more than 50% and still be able to machine therestriction by abrasive machining. Thus, the machining tool may be anabrasive machining tool.

In FIG. 7, the inserts 15 are arranged in at least a first 22 row and asecond row 23 extending along the circumference, and the first andsecond rows of inserts are arranged in succession along the longitudinalaxis. The first row 22 of inserts 15 arranged closest to the second endpart 9 has a smaller outer diameter OD₁ than the second row 23 ofinserts arranged closer to the first end part 8. The inner diameter ofthe well tubular metal structure can thereby be increased from a firstinner diameter to a second inner diameter by the first row 22 of inserts15, and from the second inner diameter to a third inner diameter by thesecond row 23 of inserts. By increasing the inner diameter ID_(s) bymeans of at least two rows 23, 23 of inserts 15, the resulting torqueand thus the power required are substantially reduced as the material tobe removed is machined in at least two steps instead of one.

In FIG. 8, each insert has a varying radial extension so that a firstpart of the insert closest to the second end part 9 of the machiningtool has a smaller radial extension than a second end part of the insertclosest to the first part 8. The machining tool thus has a smaller outerdiameter opposite the part of the inserts having a smaller radialextension, since each insert has an indentation so that the first partof the inserts contact the restriction and machine it from a firstinitial diameter to a second inner diameter and the second end part ofthe inserts machine the restriction from the second inner diameter toits final inner diameter.

In another embodiment, the inserts may be plate-shaped, have a varyingthickness and be cone-shaped. The inserts may have a varying thicknessin the radial direction so that the thickness of the inserts is greatercloser to the centre of the machining tool or the thickness may varyalong the longitudinal extension.

As can be seen in FIG. 1, the downhole wireline machining tool string 1further comprises an anchor section 31 for anchoring the string in thewell 3, and a self-propelling section 32, such as a downhole tractor,for propelling the string forward in the well. By having either theanchor section 31 or the self-propelling section 32, the tool string 1is anchored further up the well tubular metal structure 2, which meansthat all the force is transferred to the machining operation. The anchorsection 31 or the self-propelling section 32 comprises a power unit 34,such as an electrical motor, which receives power from the wireline 11.The power unit 34 drives a pump unit 35 driving the anchor section 31and/or the self-propelling section 32. The anchor section 31 and theself-propelling section 32 may have both a power unit 34 and a pump unit35. The tool string 1 may furthermore comprise one or more pressurecompensators.

FIG. 9 shows a downhole wireline machining tool string 1 for cutting outa piece, e.g. in a downhole valve. The downhole wireline machining toolstring comprises a rotatable tool part 5 comprising a machining tool 7which has a first end part 8, a second end part 9, and a stationary toolpart 6 comprising a driving unit (not shown) configured to rotate therotatable tool part and powered through a wireline. The machining tool 7comprises a body 12 ending in a drill bit 47 and having an outer face14. The machining tool 7 further comprises a fastening element 41 forfastening a machined piece 48, e.g. part of a downhole valve, such as aball-shaped valve. The fastening element 41 is circumferenting part ofthe body 12 and the body 12 is rotatable within the fastening element 41and thus the fastening means is like a union.

The fastening element 41 comprises a base part 42 and projecting parts43, and the projecting parts are more flexible than the base part sothat when the drill bit 47 of the machining tool 7 has drilled throughthe machined piece 48, the fastening element 41 is able to be squeezedinto the drilled hole in the piece 48, and thus the piece is fastened tothe machining tool without the fastening element 41 rotating along withthe rotating part 5. The body 12 of the machining tool 7 rotates withinthe fastening element 41 during the machining process, and the fasteningelement 41, when contacting the piece, does not rotate in relation tothe piece and is thus not worn. If the fastening element was to rotatealong with the rotating part of the machining tool, the projecting parts43 would be worn down, and this would cause the outer diameter of thefastening element to be slightly smaller than the inner diameter of thehole in the piece, and the fastening element would thus not be able tofasten the piece within the machining tool 7 and bring the piece tosurface along with the machining tool.

As shown in FIG. 9, the machining tool further comprises a core drill 44having a circumferential wall 45 with inserts 15 and circumferenting thebody 12 and being part of the rotatable tool part 5 for providing acircumferenting cut in e.g. a valve almost simultaneously with the drillbit machining a hole the same piece.

The projecting parts 43 are flexible and hence able to bend when beingforced into the hole just drilled by the drill bit. The projecting parts43 may have any shape suitable for fastening the piece being cut. Thefastening element 41 may also be cone-shaped, as shown in FIG. 10, sothat the piece 48 is pressed onto the inclined surface 51 of thefastening element 41 and thereby fastened. The projecting parts 43 maybe wires radially projecting from the base part or, as shown in FIG. 11,discs with radially extending arms 49 which are bent to form theprojecting parts 43. Distance elements 52 forming the base part 42 aremounted between the discs, said distance elements thus circumferentingthe body 12.

The drill bit may be constituted by inserts 15 as shown in FIG. 6, sothat the fastening element 41 is arranged around part of the body asshown in FIG. 11.

In FIG. 12, the machining tool has an internal fastening element 41 forfastening the machined piece so that the machined piece bends theprojecting parts 43 while being milled out by the drill bit 47. Once themachined piece is milled out and released from the component from whichit was previously attached to, the projecting parts 43 press towards thepiece and maintain the piece inside the machining tool. The fasteningelement 41 has projecting parts 43 which are thus flexible and henceable to bend. The projecting parts 43 are ring-shaped and spaced apartby distance elements 52 forming the base parts 42. The projecting parts43 and the distance elements 52 abut a flange 56 of the first body part57 of the body 12 and a second body part 58 is threadingly (by means ofthe thread 59) connected to the first body part pressing the projectingparts 43 and the distance elements 52 towards the flange, but does notfasten the projecting parts 43 and the distance elements 52 as they arestill able to rotate freely in relation to the body 12 so that they arenot worn down when the rotatable tool part 5 rotates the drill bit formilling out the piece. The fastening element 41 is thus arranged in thebore 17 and in the event that the machining tool is used to mill outseveral pieces, e.g. mill through a first ball resulting in a firstmachined piece and mill through a second ball further down the wellresulting in a second machined piece, the first machined piece ispressed further into the bore 17 by the second machined piece whilemilling out the second piece. The machining tool having a long bore isthus capable of milling out several balls in one run and the machinedpieces are stacked in the bore and the last machined piece is held bythe fastening element 41, closing the bore and maintaining the othermachined pieces in the bore while retracting the machining tool from thewell.

The rotatable tool part rotates at a low torque and rotates less 300revolutions per minute (RPM). The driving unit receives less than 1,000Volts or 7,000 watt due to a loss of power in the long wireline whenperforming an operation several kilometres down the well.

A stroking tool may be used to provide weight on a bit, i.e. weight onthe machining tool. The stroking tool is a tool providing an axial forcealong the longitudinal extension. The stroking tool comprises anelectrical motor for driving a pump. The pump pumps fluid into a pistonhousing in order to move a piston acting therein. The piston is arrangedon a stroker shaft. The pump may pump fluid into the piston housing onone side and simultaneously suck fluid out on the other side of thepiston.

By fluid or well fluid is meant any kind of fluid that may be present inoil or gas wells downhole, such as natural gas, oil, oil mud, crude oil,water, etc. By gas is meant any kind of gas composition present in awell, completion, or open hole, and by oil is meant any kind of oilcomposition, such as crude oil, an oil-containing fluid, etc. Gas, oil,and water fluids may thus all comprise other elements or substances thangas, oil, and/or water, respectively.

If the well is filled with gas, the downhole wireline machining toolstring may comprise a fluid delivery unit for delivering fluid to themachining area.

By a casing or well tubular metal structure 2 is meant any kind of pipe,tubing, tubular, liner, string etc. used downhole in relation to oil ornatural gas production.

In the event that the tool is not submergible all the way into the welltubular metal structure, a downhole tractor can be used to push the toolall the way into position in the well. The downhole tractor may haveprojectable arms having wheels, wherein the wheels contact the innersurface of the well tubular metal structure for propelling the tractorand the tool forward in the well tubular metal structure. A downholetractor is any kind of driving tool capable of pushing or pulling toolsin a well downhole, such as a Well Tractor®.

Although the invention has been described in the above in connectionwith preferred embodiments of the invention, it will be evident for aperson skilled in the art that several modifications are conceivablewithout departing from the invention as defined by the following claims.

1.-20. (canceled)
 21. A downhole wireline machining tool string forincreasing an inner diameter of a well tubular metal structure in awell, the downhole wireline machining tool string having a longitudinalaxis and comprising: a rotatable tool part comprising a machining toolhaving a first end part, a second end part, a diameter and acircumference, and a stationary tool part comprising: a driving unitconfigured to rotate the rotatable tool part and powered through thewireline, wherein the machining tool comprises a body having an outerface, and a plurality of inserts, each insert having a length along thelongitudinal axis, and the inserts projecting from the outer face of thebody and being distributed around the circumference.
 22. A downholewireline machining tool string according to claim 21, wherein theinserts are fastened directly to the outer face.
 23. A downhole wirelinemachining tool string according to claim 21, wherein the machining toolis an abrasive machining tool.
 24. A downhole wireline machining toolstring according to claim 21, wherein the inserts are abrasive inserts.25. A downhole wireline machining tool string according to claim 21,wherein the inserts are fastened directly to the outer face without anysupport/backing, such as a steel support.
 26. A downhole wirelinemachining tool string according to claim 21, wherein the machining toolhas a bore arranged coincident with a centre axis of the machining toolaround which the rotatable tool part rotates.
 27. A downhole wirelinemachining tool string according to claim 21, wherein each insert has awidth which is less than 40% of the length.
 28. A downhole wirelinemachining tool string according to claim 21, wherein the inserts aredistributed along the circumference with a mutual distance being atleast the width of one insert.
 29. A downhole wireline machining toolstring according to claim 21, wherein the inserts incline towards atleast one of the first and second end parts.
 30. A downhole wirelinemachining tool string according to claim 21, wherein the second end parthas a decreasing outer diameter, and at least part of the insertsextends at least partly along part of the second end part having thedecreasing outer diameter.
 31. A downhole wireline machining tool stringaccording to claim 21, wherein the inserts are arranged in at least afirst row and a second row extending along the circumference, and thefirst row and the second row of inserts are arranged in succession alongthe longitudinal axis.
 32. A downhole wireline machining tool stringaccording to claim 21, wherein the rotatable tool part rotates less than300 revolutions per minute (RPM).
 33. A downhole wireline machining toolstring according to claim 21, wherein the driving unit is powered byless than 7,000 watt.
 34. A downhole wireline machining tool stringaccording to claim 21, wherein the machining tool further comprises afastening element for fastening a machined piece, the body with insertsbeing rotatable in relation to the fastening element.
 35. A downholewireline machining tool string for increasing an inner diameter of awell tubular metal structure in a well or cutting out a piece, e.g. in adownhole valve, the downhole wireline machining tool string having alongitudinal axis and comprising: a rotatable tool part comprising amachining tool having a first end part, a second end part, a diameterand a circumference, and a stationary tool part comprising: a drivingunit configured to rotate the rotatable tool part and powered throughthe wireline, wherein the machining tool comprises a body having anouter face and a fastening element for fastening a machined piece.
 36. Adownhole wireline machining tool string according to claim 34, whereinthe body being rotatable within or around the fastening element.
 37. Adownhole wireline machining tool string according to claim 34, whereinthe fastening element comprises a base part and a projecting part, theprojecting part being more flexible than the base part.
 38. A downholewireline machining tool string according to claim 34, wherein themachining tool further comprises a core drill having a circumferentialwall with inserts, said circumferential wall circumferenting the bodyand being part of the rotatable tool part.
 39. A machining tool forincreasing an inner diameter of a well tubular metal structure in a wellor cutting out a piece, e.g. in a downhole valve, comprising: a body, aninsert forming a drill bit, a fastening element circumferenting thebody, and a core drill having a circumferential wall with inserts, saidcircumferential wall circumferenting the body.
 40. A machining toolaccording to claim 39, wherein the body being rotatable within or aroundthe fastening element.